Cannot create service due to Elastic Load Balancer Error

I would try a DependsOn in the Service resource waiting on the Listener to be created.

Service:
  Type: AWS::ECS::Service
  DependsOn: PublicLoadBalancerListener
  Properties:
    ServiceName: !Ref 'ServiceName'
  ...

The error message indicates that the target group associated with the service does not have an associated load balancer. Based on the code you provided, it seems like the service is attempting to create a new load balancer and associate it with the target group. However, it's possible that the load balancer was previously created and is no longer associated with the target group.

To fix the issue, you can try the following:

Check if a load balancer exists: You can check in the AWS Management Console to see if there is an existing load balancer. If there is, you can try to associate the load balancer with the target group.

Update the service to use an existing load balancer: If a load balancer already exists, you can modify the service YAML to use the existing load balancer instead of creating a new one. You can use the "LoadBalancerArn" property to specify the ARN of the existing load balancer.

Here is an example of how you can modify the YAML to use an existing load balancer:

Service:
Type: AWS::ECS::Service
Properties:
ServiceName: !Ref 'ServiceName'
Cluster: Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
DeploymentConfiguration:
MaximumPercent: 100
MinimumHealthyPercent: 0
DesiredCount: !Ref 'DesiredCount'
TaskDefinition: !Ref 'TaskDefinition'
NetworkConfiguration:
AwsvpcConfiguration:
Subnets:
- Fn::ImportValue: !Join [':', [!Ref 'StackName', 'PrivateSubnetOne']]
- Fn::ImportValue: !Join [':', [!Ref 'StackName', 'PrivateSubnetTwo']]
SecurityGroups: [!Ref 'PublicLoadBalancerSG']
AssignPublicIp: 'DISABLED'
LoadBalancers:
- ContainerName: !Ref 'ServiceName'
ContainerPort: !Ref 'ContainerPort'
TargetGroupArn: !Ref 'TargetGroup'

TargetGroup:
Type: AWS::ElasticLoadBalancingV2::TargetGroup
Properties:
HealthCheckProtocol: TCP
HealthCheckIntervalSeconds: 10
HealthyThresholdCount: 2
UnhealthyThresholdCount: 2
Name: !Ref 'ServiceName'
Port: !Ref 'ContainerPort'
Protocol: TCP
TargetType: ip
VpcId: Fn::ImportValue: !Join [':', [!Ref 'StackName', 'VPCId']]

PublicLoadBalancerListener:
Type: AWS::ElasticLoadBalancingV2::Listener
Properties:
DefaultActions:
- TargetGroupArn: !Ref 'TargetGroup'
Type: 'forward'
LoadBalancerArn: <existing load balancer ARN>
Port: !Ref ContainerPort
Protocol: TCP

Make sure to replace <existing load balancer ARN> with the ARN of the existing load balancer.